line arrays, widerange mid drivers, & crossovers in the "critical range"

[darkmoebius]

I've been a single/widerange(assisted) fan for about 5-7 yrs now, currently owning Hammer Dynamics Super-12's and Cain & Cain IM-Bens w/ matching Bailey subwoofers (old pics of my setup)



But, while doing research for widerange mid drivers for a line array began to question whether crossing over in the "critical range" has to be as detrimental as it is sometimes portrayed. Over the past few years, I have heard several high-end multi-way speakers who had x-o's right-smack-dab in the sacred 350-8kHz range, let alone 300-3,500Hz range, yet still seemed amazingly seamless and coherent.

Specifically, I've had several opportunities to hear:
ATC SCM150ASL (Active) monitors - Crossover Frequency : 380Hz & 3.5kHz - amazingly dynamic, powerful, and definitely some of the most accurate/transparent speakers I've ever heard.
ESP Concert Grand SI - Elliot Midwood of Acoustic Image always rolls these out at audio shows and it is nothing short of awe inspiring (for me).
Avalon Eidolon - Crossover Frequency : 300Hz & 3.5kHz - extremely smooth and seamless integration of multi-way drivers.

Now, granted, those three examples are all in the $25,000-~45,000 range, but I use them simply to show that it is possible to crossover in the "critical range" and still seemingly have coherence that we love(different, but just as engaging). I suppose this is more a matter of designer skill and implementation than sheer cost.

How does this relate to line arrays? Well, line sources are limited by the laws of "comb filtering" and lobing according to Jim Griffin's seminal paper on the subject. Center-to-center driver spacing really dictates the limitations of driver high frequency response and dispersion, no matter how good or expensive the units may be.

For midrange, a line of:
3" drivers will start to display effects at ~3.9k-4.5kHz and above(1 wavelength c-2-c) , depending on the size and shape of the driver frame.
4" at ~3,400Hz
5" at ~2,700Hz

So, I need a mid-driver capable of ~100-3.5k/4.5kHz , beyond that it really doesn't matter(Audience will strongly disagree). In fact, I have been tossing around the idea that since an x-o point is going to end up in the middle of the critical range, regardless, it might be better to trade off HF for extending the LF as close to the 80Hz omni-directional range where it can cross directly to four subwoofers like Audiokinesis' SWARM.

So, what are my (tentative) criterion? I'd like to use sealed enclosures, but could possibly be swayed towards open baffles because of room acoustics. Accuracy/transparency, dynamics, and tonality/timbre - nothing unique about that. I'd prefer a 3" driver to ease up stress of pushing the planar tweeter line too low. Low moving mass would be nice. And since I will be going for a true line of ~7 ft in height, upper limit of ~$30 per driver. (no, I won't run out and buy 60 of them on a whim. I will test a few of the finalists against each other. This is a long term project of a year or more)

Current candidates(no order of preference):
1. Tang Band TGW3-560SE 3" - these are a gamble because they are a close out of custom drivers for a speaker manufacturer who either didn't like them or abandoned the project. As of yet, I haven't found any reports from their actual use. Upside is the TB name and they do a great job of putting out FR curves that actually match their driver's performance. And the truncated driver frame is a huge bonus along with price.
2. Peerless 830987 - that's not a wizzer cone in the picture, just the inverted surround. Scaena actually uses a custom version of this driver in their $40k-80k line arrays.
3. Fountek FR88EX or FR89EX - ZaphAudio tested this driver against many, many, others and declared "This is without a doubt the highest performing 3" I've come across, at least on a few fronts."
4. Tang Band W3-1401SD - nice looking specs and FR curve, truncated frame, FS=75Hz.
5. Aurasound NS3-193-8A - lots of DIY info on this driver and seems to be a pretty reliable performer
6. Hi-Vi C3N-III 3" - a complete unknown, from what I can tell.

My questions to the community are:
1. What important specs I should be considering?
2. Which drivers above are the best performers or look most promising?
3. Are there any others I should be considering?
4. Are there standard, non-full/widerange, mid-woofers capable of ~100-3.5kHz?

[darkmoebius]

If anyone is wondering why I am posting a multi-way question here instead of that forum, it's because I'm betting far more fullrange advocates have heard well executed multi-way speakers than multi-way fans hearing well executed full/wideranges.

[kristleifur]

I want to state my interest in the project. I'll be following this one.

I also want to throw what is perhaps a spanner into the works: The Omnes BB 3.01 three-inch driver. It's juuuust over $30. Made by Tang-Band for the European Omnes Audio distributor. If Tang-Band is Toyota, this is a Lexus – solid manufacturing base, somewhat of a luxury item, but it's still cheap I don't know how easily available it is in the US, so perhaps this is not a good suggestion, but I'm impressed enough with its smoothness and clarity that I must mention it.

It's here, a little down the page: OmnesAudio-Lautsprecher

[PDRCanada]

About 2 yrs ago now I built a line array kit from Rick at Selah audio.
It incorporates 2 rows of 3" Hi-Vi drivers flanking a row of fountek ribbons.
I am very pleased with the results.....so much so that I had him design another pair using 12-4" Hi-Vi and the Dayton planers. I use these arrays
for my HT....the 3" for the fronts, the 4" for the rears. What is most remarkable about the 3"....called the Symmetricas....is the imaging and soundstage, absolutely the finest I have heard. If you would like to learn more about this design check out Selah at audiocircle.

For as nice as they sound, I use a different set up for my 2 ch listening.
A OB design by a differnt designer, using servo subs and a pro Co-ax driver.

Pics: The arrays



The OB:

[darkmoebius]

Originally Posted by PDRCanada

About 2 yrs ago now I built a line array kit from Rick at Selah audio. It incorporates 2 rows of 3" Hi-Vi drivers flanking a row of fountek ribbons...What is most remarkable about the 3"....called the Symmetricas....is the imaging and soundstage, absolutely the finest I have heard.

Aaaah, I remember the Symmetricas well, it always fascinated me. I actually traded a few posts with Rick on the old Line Array forum about the design right after he introduced it. I always wondered how the dual-line of mid drivers would affect imaging and soundstage as a result of horizontal C-to-C distancing. Rick is a truly talented designer and great guy, he always went out of his way to help DIY'ers.

For as nice as they sound, I use a different set up for my 2 ch listening.A OB design by a differnt designer, using servo subs and a pro Co-ax driver.

Brilliant design and beautiful looking speaker. There is something truly truly unique and special about the presentation of a large fullrange driver, isn't there? Is that a 12" or 15"?

I notice what looks to be a rear-firing tweeter, is there another one on the front?

Also, could you describe what is sonic difference that elevates those speakers over the Symmetricas, or even the large black planar/electrostats(?) in the background?

[PDRCanada]

The Symmetricas as I said create a huge sound stage. I was the first to purchase the kit from Rick, at the time he hadnt even finished the x-over
so he couldnt even let me know his initial impressions. I'll never forget our first conversation once he had them up....he said even his most expensive offerings didnt throw a stage like these. Imaging is also spot on, vocals and instruments...
The only thing is they are a bit colored, brass instruments sound not quite as natural as they could, although strings seem seem very realistic. To be fair I have never had them in a properly treated room.....although I have one in the works, should be done about mid Dec... so it will be a new round of critical listening once its complete.

The black planers in the back are Carver Originals. This pair was made in 1987,are absolutely mint.....have all original boxes and packaging. Why do I have these?.....a question my wife asked when I bought them a couple yrs ago. I dont really know, I just always wanted a pair since I was young. They are a nice speaker....the bass is a bit muddy and not as tight as it could be, but thats the way Bob designed them to sound he liked it like that. These are the ones I listen to loud rock music on, they need gobs of power.....I always smile and tap my foot when these are on......they really dont compare to my arrays or OB though. The highs are nice...but just not the same.

The OBs are a design by Danny Richie. This is the first offering, they have evoled a bit since this model. The driver is a 12" coaxial, by P-audio therear firing tweeter is now gone on the newer models, instead he has opened up the back and redesigned the x-over to compensate. On the bottom are 2 servo subs driven with Rythmic amps. The soundstage is not as big as the arrays, but the imaging is excellent. The two things this set up really has going for it is... natural sound, both on vocals and instrumentals. I play both woodwinds and guitar, mandoline etc....these give a very realistic presentation. The other is the tightest bass I have ever heard. Because they are OB they dont load the room, the sound is fantastic. I have a Shefield recording of solo drum performances. These make it sound like the kit is in the same room....a VERY realistic presentation.

Danny Richie was very well received this yr at RMAF with stepped up version of this OB, and Rick Craig had some bookshelves there that were outstanding. Both Rick and Danny are great designers and I am proud to have each of their offerings in my collection.

Perry

[LineArray]

Originally Posted by darkmoebius

...

But, while doing research for widerange mid drivers for a line array began to question whether crossing over in the "critical range" has to be as detrimental as it is sometimes portrayed. Over the past few years, I have heard several high-end multi-way speakers who had x-o's right-smack-dab in the sacred 350-8kHz range, let alone 300-3,500Hz range, yet still seemed amazingly seamless and coherent.

...

How does this relate to line arrays? Well, line sources are limited by the laws of "comb filtering" and lobing according to Jim Griffin's seminal paper on the subject. Center-to-center driver spacing really dictates the limitations of driver high frequency response and dispersion, no matter how good or expensive the units may be.

For midrange, a line of:
3" drivers will start to display effects at ~3.9k-4.5kHz and above(1 wavelength c-2-c) , depending on the size and shape of the driver frame.
4" at ~3,400Hz
5" at ~2,700Hz

...

If one cannot avoid interference effects due to driver
distance

-not only center to center but also "edge to edge" since
the effective cone diameter shrinks with frequency due
to non pistonic motion, making the 80% coverage
ratio proposed by Griffin impossible to achieve even for
tightly mounted fullrangers at higher frequencies -

maybe thinking about equidistant mounting being more
a problem than a solution in full- /widerange line arrays
would help ...


Interestingly the need for crossing to a tweeter
(or an array of tweeters), arises from driver
interferences and array dispersion issues, but not
necessarily from bandwith of the wide- fullrange
units being limited.

Instead of solving the problem at its root, further
problems are introduced by going multiway.

Surely kind of "good integration" could be achieved in
some multiways ... to avoid that "integrational effort" by
design seems by far more interesting to me.

Yes i see: Multiple drivers more than a wavelength apart,
cannot work, crazy guy ...

I invite you to examine the vertical dispersion of an
"dipol 08" like design in any common simulator and
compare it against equidistant line arrays due to
"useful vertical listening angles".

Assume the real driver edge to edge distances depending
on frequency, do not assume pistonic drivers, as this is
nothing but wishful thinking.

Not to talk about comparing the horizontal dispersion to
a 2-way (and two line) line array, as horizontal dispersion
often is neglected espacially when designers are too eager
to achieve a certain kind of dispersion in the vertical plane.

With "dipol 08" as an example, please note that the lower
3 drivers are continuously rolled off above above 2Khz.

Using an active solution, even the upper 3 drivers could be
reduced to one single driver in the brillance region.


Kind Regards

[darkmoebius]

Originally Posted by PDRCanada

To be fair I have never had them in a properly treated room.....although I have one in the works, should be done about mid Dec... so it will be a new round of critical listening once its complete.

Yeah, I've come to realize that in untreated rooms, we hear more of acoustic room coloration's than the speaker's true performance. I've battled my living room for years and never really won.

Originally Posted by LineArray

I invite you to examine the..."dipol 08" like design

Thank you, Oliver. I am only a few pages into your well thought out and written website, but it is extremely interesting. Sadly, I haven't used my German since leaving high school, so I have to rely on Google translate. I will read and re-read your website tonight and have plenty of questions for discussion tomorrow.

I have been intrigued by dipole and omni-directional “Coherent Wave Transmission Line Drivers” like the original Ohm Walsh A's & F's as a result year long battle with room acoustics while trying to find an optimal setup in my living for the Cain & Cains. I never was able to win that battle without extensive room treatments. It was an extremely frustrating(and expensive) experience.

BTW, there is someone who has taken Lincoln Walsh's original design, improved it, and used present day materials and computer-aided manufacturing processes to remove most, if not all, of the major problems of the original driver. Dale Harder of HHR-ExoticSpeakers is just a library of knowledge about the Walsh line source from a decades worth of repair and innovation. He says his new Walsh-type drivers can handle more power, are far more durable, have greater output and less distortion/anomalies, etc.

Here's a spec sheet comparison of his new TLS-I & TLS-II speakers versus the original Ohm Walsh A & F

[TerryO]

This is my answer to c2c distance , comb filtering and "power tapering", etc., and I've found that it works well for dedicated, critical listening situations. This is not a party speaker, not much good for PA either.

However, for solo listening, or even a couple of people, it is quite good and to quote Dr. David Hyre's remarks when he first heard them: "They're like the World's biggest headphones!"

That's not quite true, because you can move your head and the sound is still at the front of the room.



The focused array uses 12 1.5 inch "fullrange" drivers and is crossed over to an Adire Audio AV8 at 450 Hz using a series crossover. They recently took
1st place at "The Puget Sound! DIY Speaker Contest" in the 2-way class.

Best Regards,
TerryO

[LineArray]

Hello TerryO,

i truly believe your speaker having won the
price "well earned".

Nevertheless up to now nobody could ever
consistently explain to me, which specifical
problem in line arrays is solved by focussing ...

Does it contribute to uniform dispersion ?
No IMO.

Can it mitigate comb filtering in a reasonable
wide region around a "sweet spot" ?
No IMO.

Comb filtering cannot be seen independently from
spatial dispersion and listening position.
Even for straight (and also equidistant) arrays you
will find listening positions which are quite balanced ...

The problem is IMO having a fairly balanced response
for a wider range of listening positions due to angle
and distance. Any asymmetry in listener-speaker
distance will show large effects with a focussed
line array.

My personal goal would be a "good natured" behaviour
due to change of listening position in
distance/height/L-R symmetry.

Narrowing the zone of stereophonic listening, cannot
be seen as an advantage in itself IMO.

Kind Regards